Abstract TP37: Negative Diffusion-Weighted Imaging in Mild Ischemic Stroke Patients

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Background: DWI-negativity was observed in nearly one third of patients with non-disabling ischemic stroke in a recent study and complete reversal of DWI-positivity was reported in 2% of mild-moderate strokes after IV rtPA treatment. We sought to identify acute DWI-negativity and DWI reversal rates in an independent cohort treated with IV rtPA because of mild stroke symptoms (defined as NIHSS 0-5).

Methods: We reviewed a prospective single-center registry of consecutive, IV rtPA-treated patients at Aarhus University Hospital from 2004 to 2010 with a substantial number of strokes with low (0-5) NIHSS scores and reviewed their acute (<4.5 hours) and 24-hour MRI characteristics. Acute MRI is standard stroke work-up imaging at our center (except for patients with MRI contraindications). The local practice was to prefer IV rtPA treatment in mild stroke patients if clinical suspicion was supported by either MRI DWI positivity or other imaging data (MRI-perfusion lesions or visualized arterial occlusions on MRA). Only patients with final diagnoses of ischemic stroke upon hospital discharge were included in this analysis.

Results: Among 694 patients treated with IV rtPA from 2004-2010, 266 (38.3%) had NIHSS 0-5. Among these mild stroke patients, 238 received acute MRI and 107 had 24-hour follow-up MRI. Acute DWI-negativity was observed in 32/238 (13.5%; 95% CI 9.4-18.4) patients prior to IV rtPA treatment. Among the cohort with both acute and 24-hour MRIs, acute DWI-negativity was present in 15/107 (14.0%) patients and persisted in 8/15 (53.3%; 95% CI 26.6-78.7). Of 92 DWI-positive patients, only 2/92 (2.1%) became DWI-negative at 24 hours. An association of acute DWI-negativity with younger age (OR 0.98; 95% CI 0.96-1.01) or lower NIHSS (OR 0.90; 95% CI 0.69-1.18) was not found in this cohort.

Conclusions: Acute DWI-negativity was observed in ~14% of ischemic strokes with NIHSS 0-5, and half remained negative at 24 hours following IV rtPA. DWI reversal from positive to negative, possibly representing an averted infarction, occurred in 2% of patients. These rates may be lower than the true rate of DWI-negativity and reversal in mild stroke, given limitations of this analysis, including DWI-positivity influencing the initial IV rtPA decision.

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